1. Field of the Invention
The present invention relates to a method for adhesion promotion of ultra high modulus a composite consisting of polyethylene (UHMPE) fibers and epoxy resins. More particularly, the present invention relates to a process for promoting adhesion of a UHMPE fiber/epoxy resin composite.
2. Description of the Prior Art
Ultra high modulus polyethylene fibers have various utilities for the superior physical properties thereof. For example, ultra high modulus polyethylene fibers have a specific strength two times higher than that of aramid fibers; thus, they can be preferably used in the case where a high strength is required while using a small quantity. Further, the fibers have been used in the field of marine industry due to their high resistance to ultraviolet ray and salt [see, U.S. Pat. No. 4,663,101 ]. Moreover composite containing high modulus fibers has such a superior elasticity and energy absorption that no crack is happened even under overload, as well as good breaking strength [see, 33rd International SAMPE Symposium, p. 1685, 1988; and 30th National SAMPE Symposium, p. 280, 1985]. Thus, these fibers have wide range of utility beginning from various kinds of spring and ending to high pressure container, bullet proof jacket and building armature [see, U.S. Pat. Nos. 4,402,012, 4,623,574 and 4,613,535]. However, it has been reported that ultra high modulus polyethylene fiber/epoxy matrix resin composites suffer from a relatively low mechanical property, that is, delamination due to poor adhesion between the fiber and the matrix resin [see, 33rd International SAMPE Symposium, p. 721, 1988].
As an approach to overcome the above disadvantage, several methods have been proposed. In accordance with one of these approaches, the adhesion of the fiber and the matrix resin is enhanced by subjecting the surface of the fiber to a cold plasma etching treatment [see, 33rd International SAMPE Symposium, p. 551, 1988]. However, these methods suffer from the disadvantages that the functional groups on the modified surface of the fiber are deteriorated rapidly with the lapse of time; their reactivity with the matrix resin become lowered accordingly.
Another approach was the chemical treatment where the surface of ultra high modulus fibers is modified by a chromic acid solution of strong oxidizer [see, Composite Interfaces, p. 37, 1986]. However, this method may render the strength of the fiber degraded by the chromic acid used, and the wast liquid from this method may result in the environmental pollution.